Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions

You must understand the concepts described in the "Understanding Broadband Access Aggregation" module.

Optionally you may perform the preparation tasks in the "Preparing for Broadband Access Aggregation" module

Restrictions for Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions

PPP over ATM cannot be configured on IETF-compliant Logical Link Control (LLC) encapsulated PPP over ATM.

Information About Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions

PPP over ATM Configuration Scenario

PPP over ATM can be configured on all platforms running Cisco IOS Release 12.1 or later.

Note

All forms of PPP over ATM are supported on the ATM port adapters, except for the PA-A1 ATM port adapter for Cisco IOS Release 12.1. All forms of PPP over ATM are now supported on the enhanced ATM port adapter for Cisco IOS Release 12.1 or later.

The figure below shows a typical scenario for using Cisco-proprietary PPP over ATM.

Figure 1

PPP-over-ATM Network Environment

Note

If you need to configure the Cisco MGX 8220 shelf for frame forwarding at the remote sites, refer to the Cisco MGX 8220 Command Supplement for command line instructions or the Cisco StrataView Plus Operations Guide for StrataView Plus instructions. If you configure the MGX using the command line interface, use the addport and addchan commands and select frame forwarding for the port-type and chan-type arguments, respectively.

Virtual Access Interface

When you configure PPP over ATM, a logical interface known as a virtualaccessinterface associates each PPP connection with an ATM VC. You can create this logical interface by configuring an ATM permanent virtual circuit (PVC) or switched virtual circuit (SVC). This configuration encapsulates each PPP connection in a separate PVC or SVC, allowing each PPP connection to terminate at the router ATM interface as if received from a typical PPP serial interface.

The virtual access interface for each virtual circuit (VC) obtains its configuration from a virtual interface template (virtual template) when the VC is created. Before you create the ATM VC, it is recommended that you create and configure a virtual template as described in the "Preparing for Broadband Access Aggregation" module.

Once you have configured the router for PPP over ATM, the PPP subsystem starts and the router attempts to send a PPP configure request to the remote peer. If the peer does not respond, the router periodically goes into a listen state and waits for a configuration request from the peer.

The virtual access interface is associated with the VC after LCP negotiation completes. When the PPP session goes down, the virtual access interface is no longer associated with the VC and is returned to the pool of free virtual-access interfaces.

If you set a keepalive timer of the virtual template on the interface, the virtual access interface uses the PPP echo mechanism to verify the existence of the remote peer.

The following three types of PPP over ATM connections are supported:

IETF-compliant MUX encapsulated PPP over ATM

IETF-compliant LLC encapsulated PPP over ATM

Cisco-proprietary PPP over ATM

Autosense for ATM PVCs

The PPPoA/PPPoE autosense for ATM PVCs feature enables a router to distinguish between incoming PPP over ATM (PPPoA) and PPP over Ethernet (PPPoE) over ATM sessions and to create virtual access based on demand for both PPP types.

Note

The PPPoA/PPPoE autosense for ATM PVCs feature is supported on SNAP-encapsulated ATM PVCs only. It is not supported on MUX-encapsulated PVCs.

Benefits of Autosense for ATM PVCs

Autosense for ATM PVCs provides resource allocation on demand. For each permanent virtual circuit (PVC) configured for both PPPoA and PPPoE, certain resources (including one virtual-access interface) are allocated upon configuration, regardless of the existence of a PPPoA or PPPoE session on that PVC. With the autosense for ATM PVCs, resources are allocated for PPPoA and PPPoE sessions only when a client initiates a session, thus reducing overhead on the network access server (NAS).

How to Provide Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions

Configuring IETF-Compliant MUX Encapsulated PPP over ATM

Internet Engineering Task Force (IETF)-compliant multiplexer (MUX) encapsulated PPP over ATM, also known as null encapsulation, allows you to configure PPP over ATM using a VC multiplexed encapsulation mode. This feature complies with IETF RFC 2364 entitled PPP over AAL5.

You can configure ATM PVCs for IETF-compliant MUX encapsulated PPP over ATM on either point-to-point or multipoint subinterfaces. Multiple PVCs on multipoint subinterfaces significantly increase the maximum number of PPP-over-ATM sessions running on a router. You can configure IETF-compliant MUX encapsulated PPP over ATM over a single ATM PVC or an ATM PVC range.

IETF-compliant PPP over ATM is not supported on ATM SVCs and can only be applied to PVCs.

The IETF-compliant PPP over ATM feature was designed to support installations with AppleTalk Data Stream Protocol (ADSL) circuits. For an example of using ADSL termination, see the ADSL Termination Example.

Configuring IETF-Compliant LLC Encapsulated PPP over ATM

IETF-compliant LLC encapsulated PPP over ATM allows you to configure PPP over ATM with LLC encapsulation. It accommodates Frame Relay-to-ATM service interworking (Frame Relay Forum standard FRF.8). There is no equivalent VC multiplexed encapsulation mode for Frame Relay; therefore, LLC encapsulation is required for Frame Relay-to-ATM networking. This version of PPP over ATM also enables you to carry multiprotocol traffic. For example, a VC will carry both PPP and IPX traffic.

The figure below shows Frame Relay-to-ATM interworking.

Figure 2

Frame Relay-to-ATM Interworking

You can configure ATM PVCs for IETF-compliant LLC encapsulated PPP over ATM on either point-to-point or multipoint subinterfaces. Multiple PVCs on multipoint subinterfaces significantly increase the maximum number of PPP-over-ATM sessions running on a router.

You can also configure IETF-compliant LLC encapsulated PPP over ATM in a VC class and apply this VC class to an ATM VC, subinterface, or interface. For information about configuring a VC class, refer to the section "Configuring VC Classes" in the module "Configuring ATM."

Note

Depending on whether you configure IETF-compliant LLC encapsulated PPP over ATM directly on a PVC or interface, your PVC will inherit the configuration that takes highest precedence. For a description of the inheritance hierarchy, see the protocol command in the Cisco IOS Wide-Area Networking Command Reference Guide.

Perform this task to configure IETF-compliant LLC encapsulated PPP over ATM on a PVC or range of PVCs.

SUMMARY STEPS

1.enable

2.configureterminal

3.Do one of the following:

interfaceatmslot/port.subinterface-numberpoint-to-point

or

interfaceatmnumber.subinterface-numberpoint-to-point

interfaceatmslot/port.subinterface-numbermultipoint

or

interfaceatmnumber.subinterface-numbermultipoint

4.Do one of the following:

pvc [name] vpi/vci

range [range-name] pvcstart-vpi/start-vciend-vpi/end-vci

5.encapsulationaal15snap

6. protocol ppp virtual-template number

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

Do one of the following:

interfaceatmslot/port.subinterface-numberpoint-to-point

or

interfaceatmnumber.subinterface-numberpoint-to-point

interfaceatmslot/port.subinterface-numbermultipoint

or

interfaceatmnumber.subinterface-numbermultipoint

Example:

Router(config)# interface atm 6/0.200 point-to-point

Example:

Router(config)# interface atm 1/0/0.4 multipoint

Specifies the ATM point-to-point or multipoint subinterface using the appropriate format of the interfaceatm command.2

3 "SNAP encapsulation" is a misnomer here, since this encapsulation configures both LLC and SNAP encapsulation on the VC. If SNAP encapsulation is not configured at a lower inheritance level, or another type of encapsulation is configured at a lower inheritance level, you will have to configure both SNAP and the protocol ppp command to ensure that PPP over ATM with LLC encapsulation is configured on your VC.

Configuring Cisco-Proprietary PPP over ATM PVCs

You can configure ATM PVCs for Cisco-proprietary PPP over ATM on either point-to-point or multipoint subinterfaces. Configuring multiple PVCs on multiple subinterfaces significantly increases the maximum number of PPP-over-ATM sessions running on a router. Remote branch offices must have Cisco-proprietary PPP over ATM configured on PPP-compatible devices interconnecting directly to Cisco's ATM Switch Interface Shelf (AXIS) equipment through a leased-line connection. The shelves provide frame forwarding encapsulation and are terminated on BPX cores prior to connecting to a Cisco 7500 series router.

Perform this task to configure Cisco-proprietary PPP over ATM on a PVC or range of PVCs.

SUMMARY STEPS

1.enable

2.configureterminal

3.Do one of the following:

interfaceatmslot/port.subinterface-numberpoint-to-point

or

interfaceatmnumber.subinterface-numberpoint-to-point

interfaceatmslot/port.subinterface-numbermultipoint

interfaceatmnumber.subinterface-numbermultipoint

4.Do one of the following:

pvc [name] vpi/vci

range [range-name] pvcstart-vpi/start-vciend-vpi/end-vci

5.encapsulationaal5ciscopppvirtual-templatenumber

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

Do one of the following:

interfaceatmslot/port.subinterface-numberpoint-to-point

or

interfaceatmnumber.subinterface-numberpoint-to-point

interfaceatmslot/port.subinterface-numbermultipoint

interfaceatmnumber.subinterface-numbermultipoint

Example:

Router(config)# interface atm 6/0.200 point-to-point

Example:

Example:

Example:

Router(config)# interface atm 1/0/0.4 multipoint

Specifies the ATM point-to-point or multipoint subinterface using the appropriate format of the interfaceatm command.4

Configuring SVCs for NAPs and NSPs

When PPP over ATM is configured over an SVC rather than a PVC, an ATM SVC is established using a configured ATM address each time an end user initiates a connection to a Network Access Provider (NAP) or Network Service Provider (NSP). A PPP session is then established over the SVC. By using PPP, the NAPs and NSPs can authenticate users and provide suitable access to the various services being offered. Whereas PVCs require that services and destination addresses be predetermined, using PPP over ATM SVCs allows users to choose services and the quality of those services dynamically on the basis of the destination address.

The figure below shows a typical network topology for PPP over ATM SVCs terminating at an NAP.

Figure 3

PPP over ATM SVC Terminating at a Network Access Provider

The figure below shows a typical network topology of PPP over ATM SVCs terminating at an NSP.

Figure 4

PPP over ATM SVC Terminating at a Network Service Provider

The PPP over ATM SVCs feature works by associating each PPP session with a virtual-access interface. Each virtual-access interface is associated with an SVC. The SVCs use static maps that hold information about the encapsulation type and virtual template number. A single static map can accept multiple PPP over ATM SVC calls.

Perform this task to configure PPP over an ATM SVC.

SUMMARY STEPS

1.enable

2.configureterminal

3.Do one of the following:

interfaceatmslot/port.subinterface-numberpoint-to-point

or

interfaceatmnumber.subinterface-numberpoint-to-point

interfaceatmslot/port.subinterface-numbermultipoint

interfaceatmnumber.subinterface-numbermultipoint

4.svc[name]

5.encapsulationaal5auto

6.protocolpppvirtual-templatenumber

7.maxvcnumber

8.maxbandwidthkbps

9.exit

10.exit

11.atmnsap-addressnsap-address

12. exit

13.showatmsvc

14.showatmsvcppp

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

Do one of the following:

interfaceatmslot/port.subinterface-numberpoint-to-point

or

interfaceatmnumber.subinterface-numberpoint-to-point

interfaceatmslot/port.subinterface-numbermultipoint

interfaceatmnumber.subinterface-numbermultipoint

Example:

Router(config)# interface atm 6/0.200 point-to-point

Example:

Example:

Example:

Router(config)# interface atm 1/0/0.4 multipoint

Specifies the ATM point-to-point or multipoint subinterface using the appropriate format of the interfaceatm command.5

Step 4

svc[name]

Example:

Router(config-subif)# svc cisco

Configures the SVC.

Step 5

encapsulationaal5auto

Example:

Router(config-subif-atm-vc)# encapsulation aal5auto

Specifies encapsulation auto, which allows the SVC to use either aal5snap or aal5mux encapsulation types.

Step 6

protocolpppvirtual-templatenumber

Example:

Router(config-subif-atm-vc)# protocol ppp virtual-template 6

Specifies that PPP is established over the ATM SVC using the configuration from the specified virtual template.

Step 7

maxvcnumber

Example:

Router(config-subif-atm-vc)# max vc 5

Specifies the maximum number of SVCs that can be established using the current configuration.

Step 8

maxbandwidthkbps

Example:

Router(config-subif-atm-vc)# max bandwidth 564

Specifies the total amount of bandwidth available to all SVCs in the current configuration.

Verifying PPPoA Autosense for ATM PVCs

After the client at the other end of the PVC has initiated a PPPoA session, use this command to check that the PVC contains the PPPoA session.

Step 2

showcaller

Use this command to:

View individual users and consumed resources on the NAS.

Inspect active call statistics for large pools of connections. (The debug commands produce too much output and tax the CPU too heavily.)

Display the absolute and idle times for each user. The current values for both of these settings are displayed on the TTY line and the asynchronous interface. Users that have been idle for unacceptably long periods of time can be easily identified. By using this information, you can define time-out policies and multiple grades of services for different users.

IETF-Compliant PPP over ATM with Different Traffic-Shaping Parameters Example

PVCs with different PPP-over-ATM traffic-shaping parameters can be configured on the same subinterface. In the following example, three PVCs are configured for PPP over ATM on subinterface ATM 2/0.1. PVC 0/60 is configured with IETF-compliant PPP over ATM encapsulation. Its traffic-shaping parameter is an unspecified bit rate with peak cell rate at 500 kbps. PVC 0/70 is also configured with IETF-compliant PPP over ATM encapsulation, but its traffic-shaping parameter is nonreal-time variable bit rate, with peak cell rate at 1 Mbps, sustainable cell rate at 500 kbps, and burst cell size of 64 cells. PVC 0/80 is configured with the Cisco-proprietary PPP over ATM encapsulation. Its traffic-shaping parameter is an unspecified bit rate with peak cell rate at 700 kbps. For further information, refer to the Configuring IETF-Compliant MUX Encapsulated PPP over ATM earlier in this module.

ADSL Termination Example

The IETF-Compliant PPP over ATM feature was designed to support installations with asymmetric digital subscriber line (ADSL) circuits. The figure below illustrates a topology for ADSL termination. This topology allows you to establish a PPP connection to a Cisco 7200 series router.

The example also illustrates the use of PPP tunneling using L2TP to provide VPDN services, in this case for the domain cisco.com. Thus, a user who logs in as bob2257@cisco.com is automatically tunneled to IP address 10.1.2.3. (See the module "Configuring Virtual Private Networks" in the Cisco IOS VPDN Configuration Guide for details about setting up VPDN services.)

Two Routers with Back-to-Back PVCs Example

The figure below illustrates an ATM interface with two PPP sessions over two PVC session connections. (See the module "PPP Configuration" in the CiscoIOSDialTechnologiesConfigurationGuide for details on PPP configuration.) The sample commands following the figure below establish the back-to-back router configuration. For further information, refer to the Configuring IETF-Compliant MUX Encapsulated PPP over ATM earlier in this module.

Multiplexed Encapsulation Using VC Class Example

In the following example, PVC 0/60 is configured on subinterface ATM 2/0.1 with a VC class attached to it. For details on creating and applying a VC class, see the section "Configuring VC Classes" in the module "Configuring ATM." By rule of inheritance, PVC 0/60 runs with IETF-compliant PPP over ATM encapsulation using the configuration from interface virtual-template 1. Its parameter is an unspecified bit rate with peak cell at 90 kbps.

Overriding a Virtual Template for IETF-Compliant PPP over ATM Example

This example illustrates how to use inheritance to override a virtual template configuration for muxppp or ciscoppp encapsulation options. For PVC 5/505, since the encapsulation option at that level is ciscoppp virtual template 1, as specified in the VC class called muxppp, the protocolpppvirtual-template2 command overrides only the virtual-template configuration. For further information, refer to the IETF-Compliant LLC Encapsulated PPP over ATM Configuration Examples.

This example shows how to limit the configuration of a particular LLC encapsulated protocol to a particular VC. First, we see that the VC class called "ppp" is configured with IETF PPP over ATM with LLC encapsulation and virtual template 1. This VC class is then applied to ATM interface 1/0/0. By configuring SNAP encapsulation by itself on PVC 0/32, you disable IETF PPP over ATM with LLC encapsulation on this particular PVC; PVC 0/32 will only carry IP. For further information, refer to the IETF-Compliant LLC Encapsulated PPP over ATM Configuration Examples.

Cisco Proprietary-PPP-over-ATM Example

The following example shows how to configure Cisco-proprietary PPP over ATM to use PPP unnumbered link and Challenge Handshake Authentication Protocol (CHAP) authentication. For further information, refer to the Configuring Cisco-Proprietary PPP over ATM PVCs.

PPP over an ATM SVC Configuration Example

In the following example, ATM interface 2/0/0 is configured to accept ATM SVC calls whose called party address is 47.00918100000000400B0A2501.0060837B4740.00. The same ATM NSAP address can be configured on other physical ATM interfaces as well. When a PPP session is established, a virtual-access interface is created and cloned with the configuration from virtual template 1. All PPP sessions established on this ATM interface will use the IP address of loopback interface 0. A maximum of 100 SVCs can be established using this configuration. SVCs established using this configuration cannot take up more than 50 Mbps in total bandwidth.

Effective with Cisco IOS Release 12.2(28)SB, the pppoelimitper-mac and pppoelimitper-vc commands are replaced by the sessionsper-maclimit and sessionsper-vclimit commands, respectively, in bba-group configuration mode. See the sessionsper-maclimit and sessionsper-vclimit commands for more information.

In the following example, PPPoA and PPPoE sessions are handled separately by two virtual templates.

Whenever possible, it is preferable to configure PPPoA and PPPoE to use the same virtual template. Using separate virtual templates leads to the inefficient use of virtual access because the maximum number of virtual-access interfaces will have to be precloned twice: once for PPPoE and once for PPPoA. If PPPoA and PPPoE use the same virtual template, the maximum number of virtual-access interfaces can be precloned once and used for PPPoA and PPPoE as needed.

Where to Go Next

If you want to identify a physical subscriber line for RADIUS communication with a RADIUS server, refer to the "Identifying a Physical Subscriber Line for RADIUS Access and Accounting" module.

Additional References

The following sections provide references related to providing protocol support for broadband access aggregation of PPP over ATM sessions.

Related Documents

Related Topic

Document Title

Broadband access aggregation concepts

Understanding Broadband Access Aggregation

Broadband access aggregation preparation tasks

Preparing for Broadband Access Aggregation

Standards

Standards

Title

Frame Relay Forum standard FRF.8

Frame Relay to ATM Internetworking

MIBs

MIBs

MIBs Link

None

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

RFCs

RFCs

Title

RFC 2364

PPP over AAL5

Technical Assistance

Description

Link

The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

Feature Information for Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1

Feature Information for Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions

The PPPoA/PPPoE autosense for ATM PVCs feature enables a router to distinguish between incoming PPP over ATM (PPPoA) and PPP over Ethernet (PPPoE) over ATM sessions and to create virtual access based on demand for both PPP types.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

3 "SNAP encapsulation" is a misnomer here, since this encapsulation configures both LLC and SNAP encapsulation on the VC. If SNAP encapsulation is not configured at a lower inheritance level, or another type of encapsulation is configured at a lower inheritance level, you will have to configure both SNAP and the protocol ppp command to ensure that PPP over ATM with LLC encapsulation is configured on your VC.